String path=request.getRealPath("/");//传递参数"/"可以返回web应用根目录
String tmp_path=path+"tmp";
File f1=new File(tmp_path);//创建FILE类,指定路径为tmp_path
f1.mkdir();//创建目录
File f2=new File(tmp_path,"a.txt");//创建FILE类,指定路径为//tmp_path+"a.txt"
f2.createNewFile();//创建f2指定的文件
File f3=new File(tmp_path,"b.txt");
f3.createNewFile();
File f4=new File(tmp_path,"b.txt");
f4.createNewFile();

String path=request.getRealPath("/");
File fp=new File(path,"file1.txt");//定义一个文件
FileInputStream fistream=new FileInputStream(fp);//定义一个文件输入流绑定一个文件
byte buf[]=new byte[10000];
int bytesum=fistream.read(buf,0,10000)//把字节文件写入到buf数组中,返回写入的字节数
String str_file=new String(buf,0,bytesum);
out.println(str_file);
fistream.close();

String path=request.getRealPath("/");
File fp=new File(path,"file1.txt");
FileReader freader=new FileReader(fp):
BufferedReader bfdreader=new BufferedReader(freader);
String str_line=bfdreader.readLine();
while(str_line!=null){
  out.println(str_line);
  out.println("<br>");
  str_line=bfdreader.readLine();
 }
 bfdreader.close();
 freader.close();

String path=request.getRealPath("/");
File fp=new File(path,"file2.txt");
FileWriter fwriter=new FileWriter(fp);
request.setCharacterEncoding("GBK");//设置字符编码
String str_file=request.getParameter("textarea");
fwriter.write(str_file);
fwriter.close();

String path=request.getRealPath("/");
File fp=new FIle(path,"file2.txt");
FileWriter fwriter=new FIleWriter(fp);
BufferedWriter bfwriter=new BufferedWriter(fwriter);
request.setCharacterEncoding("GBK");
String str_file=request.getParameter("textarea");
bfwriter.write(str_file,0,str_file.length());
bfwriter.flush();
bfwriter.close();